Regular expression for letters numbers and -

Question

I m having trouble checking in PHP if a value is is any of the following combinations   letters  upper or lowercase  numbers  0-9  underscore     dash  -  point     no spaces  or other characters   a few examples    OK   screen123 css  OK   screen-new-file css  OK   screen new js  NOT OK   screen new file css    I guess I need a regex for this  since I need to throw an error when a give string has other characters in it than the ones mentioned above

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A-Za-z0-9  -    This will also match for empty strings  if you do not want that exchange the last   for an

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w-        What is  means By     Start of string           Match characters inside   w Any word character so 0-9 a-z A-Z  -   Matched by charecter - and   and    Zero or more of pattern or unlimited   End of string If you want to limit the amount of characters      w-    0 5      0 5  Means 0-5  Numbers  amp  characters

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The pattern you want is something like  see it on rubular com      a-zA-Z0-9  -      Explanation      is the beginning of the line anchor   is the end of the line anchor       is a character class definition   is  zero-or-more  repetition   Note that the literal dash - is the last character in the character class definition  otherwise it has a different meaning  i e  range   The   also has a different meaning outside character class definitions  but inside  it s just a literal    References   regular-expressions info Anchors  Character Classes and Repetition     In PHP  Here s a snippet to show how you can use this pattern    lt  php   arr   array     screen123 css      screen-new-file css      screen new js      screen new file css      foreach   arr as  s      if  preg match      w -        s         print   s is a match n       else       print   s is NO match    n             gt    The above prints  as seen on ideone com    screen123 css is a match screen-new-file css is a match screen new js is a match screen new file css is NO match      Note that the pattern is slightly different  using  w instead  This is the character class for  word character    API references   preg match     Note on specification  This seems to follow your specification  but note that this will match things like        etc  which may or may not be what you desire  If you can be more specific what pattern you want to match  the regex will be slightly more complicated   The above regex also matches the empty string  If you need at least one character  then use    one-or-more  instead of    zero-or-more  for repetition   In any case  you can further clarify your specification  always helps when asking regex question   but hopefully you can also learn how to write the pattern yourself given the above information

User · Answer

you can use    w -     the   is to make sure it has at least 1 character   Need the   and   to denote the begin and end  otherwise if the string has a match in the middle  such as     xyz     then it is still a match   w already includes alphabets  upper and lower case   numbers  and underscore  So the rest    -  are just put into the  quot class quot  to match   The   means 1 occurrence or more  P S  thanks for the note in the comment

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Something like this should work   code    screen new file css   if   preg match     - a-zA-Z0-9         code         echo  not valid       This will echo  not valid

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This is the pattern you are looking for      w-         What this means      Start of string       Match characters inside  w Any word character so 0-9 a-z A-Z -   Match - and   and     Zero or more of pattern or unlimited    End of string   If you want to limit the amount of characters       w-    0 5       0 5  Means 0-5 characters

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To actually cover your pattern  i e  valid file names according to your rules  I think that you need a little more   Note this doesn t match legal file names from a system perspective   That would be system dependent and more liberal in what it accepts   This is intended to match your acceptable patterns      a-zA-Z0-9    -    a-zA-Z0-9     a-zA-Z0-9      Explanation      Match the start of a string   This  plus the end match  forces the string to conform to the exact expression  not merely contain a substring matching the expression    a-zA-Z0-9    -    Zero or more occurrences of one or more letters or numbers followed by an underscore or dash   This causes all names that contain a dash or underscore to have letters or numbers between them   a-zA-Z0-9   One or more letters or numbers   This covers all names that do not contain an underscore or a dash     A literal period  dot    Forces the file name to have an extension and  by exclusion from the rest of the pattern  only allow the period to be used between the name and the extension   If you want more than one extension that could be handled as well using the same technique as for the dash underscore  just at the end   a-zA-Z0-9   One or more letters or numbers   The extension must be at least one character long and must contain only letters and numbers   This is typical  but if you wanted allow underscores  that could be addressed as well   You could also supply a length range  2 3  instead of the one or more   matcher  if that were more appropriate    Match the end of the string   See the starting character

[regex] Regular expression for letters, numbers and - _

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